I recently signed two new buyer clients and upon my asking them why they called me, they said I was the only one who handed out my business cards when they were attending one of my open houses. Even if it's not my listing, I bring along my cards and make them available next to the sign-up sheet and hand them out to people who say they aren't yet working with an agent.
I was very surprised by this. It seems to me it's one of the primary reasons for the non-listing agent to cover an open house (aside from selling the property). My clients said they attended five open houses that weekend and because I was the only one who spoke with them and gave them my card, I'm the only one they remembered.